"Do I have to remove all the grout? Can I just deep clean it to kill any mold and then top coat?"

Top coat with what?

New grout

If your going to regrout, the old grout needs to be removed.

Grout never comes up flush to the top of the tile. That looks like a standard tile install. Maybe you should talk to your Dr. about the foot sensitivity.

This grout doesn’t come up to the proper level. The walls are done correctly. Don’t appreciate your snark. I’m interested in how to remove the existing grout without spending days using a grout saw on hundred of tiny mosaic grout joint.

" I’m interested in how to remove the existing grout without spending days using a grout saw on hundred of tiny mosaic grout joint. "

Dremel orhere are a few other tools for removing grout. It will not be easy and it will be messy but if you do not remove it you will in fairly short order be removing the new grout plus the existing grout.

Thank you for the Dremel idea. Yes this is the correct solution. I’ll hire someone to do the removal and regrouting and the final sealing.

If Mapei FlexColor CQ grout was used, my understanding is that extra grout can be added right on top of existing grout without removing any of the current grout (learned that here on Houzz from some pros). Longshot probably - but thought I’d let you know just in case!

Q - it looks like you had genuine marble installed - is that correct? Have you had any issues with discolorarion due to water retention on your floor?

Thank you but unfortunately we moved into this house recently and have no idea what grout was used. Looks like marble but is tile so not discoloration. Really bad grout installation but at least the former owner only used real marble on the vanity tops and kitchen island and countertops. ;)

The grout redo suggestion was given as a DIY job, because that's the only way it makes any sense to do. If you are going to pay labor, it will be cheaper to do a tear out and redo than having someone gouge out the tiny little grout lines on a 1x1 mosaic pan. And that will likely result in chipped marble as well. So live with it, until you can redo the pan. The redo of the pan is not going to be warrantied, and how it's redone will depend on what waterproofing system was used. As will the cost of that. A couple of thousand, at least.